Styrene is commercially produced by two main processes: (1) the dehydrogenation of ethyl benzene; and (2) the dehydration of 1-phenyl ethanol. The most commercially successful process to produce styrene utilizing the dehydration of 1-phenyl ethanol has been the process for the co-production of propylene oxide and styrene monomer (the “POSM process”). The POSM process involves the oxidation of ethyl benzene to form ethyl benzene hydroperoxide, the catalytic reaction of the hydroperoxide with propylene to form propylene oxide and 1-phenyl ethanol, and the dehydration of the 1-phenyl ethanol to produce styrene monomer. A patent describing this process is U.S. Pat. No. 3,351,635.
The dehydration of 1-phenyl ethanol is a well known reaction. The dehydration process can be performed in the vapor phase and the liquid phase. For example, the vapor phase dehydration of 1-phenyl ethanol is described in U.S. Pat. Nos. 3,442,963 and 3,658,928, and the liquid phase dehydration is described, for example, in U.S. Pat. No. 3,526,674.
Vapor phase dehydration processes typically employ solid catalysts such as titania or alumina. However, these solid catalysts often require frequent regenerations to maintain acceptable conversion and selectivity at high levels. From the standpoint of economics and efficiencies of operation, it is often advantageous to conduct the 1-phenyl ethanol dehydration in the liquid phase in the presence of appropriate catalysts. Although solid catalysts are also useful in the liquid phase dehydration processes, it is preferred to use homogeneous acids such as sulfuric acid, phosphoric acid, and p-toluenesulfonic acid (see, e.g., U.S. Pat. No. 3,526,674). A disadvantage of such technologies is that a certain percentage of the feed material is converted to undesirable by-products such as heavy condensation products, thus lowering the efficiency of the dehydration reaction.
U.S. Pat. No. 5,639,928 describes an improved liquid phase dehydration of 1-phenyl ethanol to styrene monomer. The improvement comprises the use of a residue formation inhibiting agent (nitro substituted phenol or nitro substituted sulfonic acid) during the liquid phase dehydration.
In sum, new and improved processes for the dehydration of 1-phenyl ethanol are needed.